Procedure for operating an exhaust gas treatment device and the device for implementing the procedure

ABSTRACT

A procedure for operating an exhaust gas treatment device arranged in the exhaust gas area of a combustion engine, which requires for the catalytically supported conversion of the NOx emission of the combustion engine a reagent, whose dosage is determined by a dosage signal depending on a NOx actual value that is contained in the exhaust gas treatment device and that is measured by a NOx sensor, which is contained in the exhaust gas treatment device downstream after a catalyzer, as well as a device for implementing the procedure is suggested. The dosage singal is influenced by a correcting signal depending on a measure for the operating time of the exhaust gas treatment device in the sense of an increase of the dosage of the reagent. The strategy according to the invention allows the condsideration of a long-term drift of the NOx emissions of the combustion engine and/or of long-term drifts of individual drifts of the exhaust gas treatment device and ensures a preset minimum NOx conversion rate for the entire operating time of the exhaust gas treatment device.

STATE OF THE ART

The invention is based on a procedure for operating an exhaust gas treatment device, which requires one reagent for the catalytic conversion of at least NOx, and on the device for implementing this procedure according to the category of independent claims.

The subject matter of the present invention is also a controller program and a controller program product.

In DE 199 03 439 A1 a procedure is described for operating a combustion engine, in whose exhaust gas area a SCR catalyzer (selective-catalytic-reduction) is arranged, which reduces the nitrous gases that are contained in the exhaust gas of the combustion engine with a reagent to nitrogen. The dosage of the reagent or a prestage of the reagent takes place preferably depending on parameters of the combustion engine, as for example the engine speed and fuel quantity that has been injected, which can at least be used as a measure for the nitrous gases that have been emitted by the combustion engine. Furthermore the dosage preferably takes place depending on exhaust gas parameters, as for example the exhaust gas temperature and/or the operating temperature of the SCR catalyzer. As a reagent for example the reducing agent ammoniac is provided, which can be acquired from a urea-water solution as a prestage of the reagent. The dosage of the reagent has to be determined accurately. A too low dosage implicates that nitrous gases cannot be completely reduced anymore. A too high dosage leads to a reagent slip, which can cause unnecessary high reagent consumption on the one hand and an aggravating odor nuisance depending on the consistency of the reagent on the other hand.

In DE 10 2004 031 624 A1 a procedure is described for operating a SCR catalyzer that is used for cleaning the exhaust gas of a combustion engine, at which a controlling or regulation of the reagent filling-level in the SCR catalyzer is provided on a determined store nominal value. The determination of the store nominal value ensures that in unsteady statuses of the combustion engine a sufficient amount of reagent is provided for the complete elimination of the NOx-crude emission of the combustion engine on the one hand, and that a reagent slip is broadly prevented on the other hand. The reagent filling-level in the SCR catalyzer is determined with the aid of a catalyzer model, which considers the NOx mass flow that flows into the SCR catalyzer, the NOx mass flow that flows out of the SCR catalyzer, the catalyzer temperature as well as the reagent slip where necessary. The maximum possible reagent filling-level of the SCR catalyzer depends especially on the operating temperature of the catalyzer, which is the highest at low operating temperatures and drops to lower figures with increasing operating temperatures. The level of efficiency of the SCR catalyzer depends on the catalytic activity, which is lower at lower operating temperatures, passes a maximum with higher operating temperatures and drops again with further increasing operating temperatures.

In DE 10 2005 042 489 A1 (not published) a procedure is described for operating a combustion engine, in whose exhaust gas area a SCR catalyzer is arranged, which is impinged with a reagent that contributes to the conversion of NOx. The NOx concentration that occurs downstream after the catalyzer is measured with a NOx sensor, which has a cross sensitivity towards the reagent, for example ammoniac. The measured NOx concentration is compared to a calculated NOx concentration. Depending on the difference it is intervened in the dosage of the reagent. A plausibilization is provided, at which the reagent quantity that is dosed in a preset period of time and the reagent quantity that is converted in the SCR catalyzer and/or the converted NOx concentration are compared to each other. Due to the cross sensitivity of the NOx sensor towards the reagent at a fixed difference, it cannot be decided without further ado, whether an overdosing or underdosing of the reagent is present, so the plausibilization is provided, which allows a statement about the undertaken correction of the dosage.

A similar strategy has become known from DE 10 2006 041 676 A1 (not published), at which a comparison of the difference between a calculated and a measured NOx concentration downstream after a SCR catalyzer with a difference threshold is also provided. At an exceeding of a difference threshold a measure for lowering or complete abatement of the dosage is adopted. Subsequently the difference is checked for a dosage for an increase, whereby then, if the difference exceeds the mass for the increase, a measure for the increase of the dosage is adopted.

In DE 10 205 042 490 A1 (not published) a procedure is also described for operating a combustion engine, in whose exhaust gas area at least one SCR catalyzer is arranged, which is impinged with a reagent, which contributes to the NOx conversion. A plausibilization for the difference between the measured dosage for the NOx concentration downstream after the catalyzer and a calculated dosage is provided. It is assumed that the NOx sensor has a cross sensitivity towards the reagent. The ascertained differences are each evaluated. Depending on the results of the evaluation it is intervened in the determination of the reagent signal. With the described measures a long term adaptation of the reagent signal is achieved.

A similar strategy became known from DE 10 2005 042 487 A1 (not published), at which a dosage for the NOx concentration that occurs downstream after the catalyzer is also calculated and measured with NOx sensor that is cross sensitive towards the reagent. A regularization of the reagent filling-level in the SCR catalyzer on a threshold is assumed. A plausibilization of the sensor signal can take place by a simple overdosing of the reagent, at which it is proceeded on the assumption that there is a maximum possible reagent filling-level in the catalyzer. In this operating status of the catalyzer it can be implied that the NOx sensor detects the reagent slip. By an intervention in the target-filling-level of the reagent in the catalyzer depending on the ascertained difference between the calculated and the measured NOx concentration a short-term adaptation of the dosage can be achieved, which corresponds with the short term adaptation.

Currently available NOx sensors show tolerances with regard to the accuracy of measurement, which can influence the measurement results regarding the always stricter becoming exhaust gas regulations. Specifically it has to be assumed that the NOx sensors show a long term drift, which influences the accuracy of measurement. Additionally or alternatively to the drift of a NOx sensor a drift of a reagent insertion device and/or an ageing of a catalyzer and/or a change of the NOx emissions of a combustion engine can cause that a preset minimum NOx conversion rate of the exhaust gas treatment device is not adhered anymore.

The invention is based on the task to approach a procedure for operating an exhaust gas treatment device as well as a device for implementing the procedure, which ensures a preset minimum NOx conversion over the entire operating time of the exhaust gas treatment device.

The task is solved by the features that are indicated in the independent claims.

DISCLOSURE OF THE INVENTION

According to the invention it is provided that a dosage signal, which determines the dosage of the reagent depending on a dosage for the operating time of the exhaust gas treatment device in the sense of an increase of the dosage of the reagent at a advancing operating time of the exhaust gas treatment device, is influenced by a correction signal.

The measure that is adopted according to the invention ensures the required minimum NOx conversion over the entire operating time of the exhaust gas treatment device. A drift that may occur, especially a long term drift of the NOx sensor and/or of a reagent insertion combustion engine is compensated with the measure that is adopted according to the invention.

The strategy according to the invention is based on the realization that due to the tolerances or drifts of individual components of the exhaust gas treatment device and/or due to changes of the NOx emissions of a combustion engine even with a NOx sensor that works within a specified accuracy already an insufficient NOx conversion in the exhaust gas treatment device can occur. At the activation of the exhaust gas treatment device tolerances can be considered within the scope of the application. At a posterior operation of the exhaust gas treatment device such an intervention for compensating drifts is not possible anymore without further ado. The strategy according to the invention provides tendentially for a simple overdosing of the reagent in order to be able to comply with the preset minimum NOx conversion rate. But an unnecessary overdosing of the reagent has not to be accepted, since the NOx sensor provides a sensor signal for the reagent at a possible overdose of the reagent due to a cross sensitivity towards the reagent, with which the overdose within the scope of a regularization or rather an adaptation can be worked against. Short term reagent slip peaks are also registered by the NOx sensor that is tolerance afflicted.

Advantageous improvements and embodiments according to the invention emerge from the dependent claims.

One embodiment provides that the dosage signal is pre-controlled and regulated. The pre-controlling takes place for example with the aid of a calculated reagent filling-level in the catalyzer. The reagent filling-level is determined expediently with the aid of a catalyzer model. The catalyzer model considers preferably at least the catalyzer temperature as well as a dosage for the NOx mass flow.

According to one embodiment it is provided that the difference between a dosage for the measured NOx concentration and a NOx nominal value is regulated. The ascertained difference is preferably used to influence the calculated reagent filling-level in the catalyzer.

One embodiment provides a short term adaptation, which intervenes in the catalyzer model during the calculation of the reagent filling-level. Alternatively or additionally a long term adaptation is preferably provided, from which the dosage signal is ascertained.

One embodiment provides that the driven kilometers of a motor vehicle are used as a dosage for the operating time of the NOx sensor, in which the combustion engine is used as a power train.

The correction signal is preferably fixed to a value range of 1.0 to 1.2, so that the correction signal is applicable for a multiplicative connection.

According to the invention the device for implementing the procedure is initially based on a controller that is customized for the implementation of the procedure.

The controller contains preferably at least one electric storage, in which the steps of the procedure are stored as a controller program.

According to the invention the controller program provides that all steps of the procedure according to the invention are implemented, if it runs in a controller.

According to the invention the controller program product with a program code, which is stored on a machine readable medium implements the procedure according to the invention, if the program takes place in a controller.

Further advantageous improvements and embodiments of the strategy according to the invention follow from further dependent claims. Embodiments of the invention are shown in the drawing and are explained in the following description.

It shows:

FIG. 1 a technical environment, in which a procedure according to the invention takes place and

FIG. 2 a relation between a dosage signal and a NOx concentration downstream after a catalyzer or rather a relation between the dosage signal and a reagent slip.

FIG. 1 shows a combustion engine 10, in whose exhaust gas area 12 a reagent insertion device 14 as well as at least one catalyzer 16 are arranged. A NOx emission NOx_vK of the combustion engine 10 and a NOx concentration NOx_nK after the catalyzer 16 occur in the exhaust gas area 12.

Downstream after the catalyzer 16 a NOx sensor 18 is provided, which provides a controller 20 with a dosage for the NOx concentration NOx_nK as a NOx actual value NOx_Mes. The reagent insertion device 14, the catalyzer 16 and the NOx sensor 18 compose altogether the exhaust gas treatment device 14, 16, 18.

The controller 20 provides a reagent dosage 14 and a dosage signal s_D.

The combustion engine 10 emits an off-gas stream, which contains the NOx emissions NOx_vK. The NOx parts in the exhaust gas shall be converted in the catalyzer 16 into less damaging exhaust gas components. For this purpose the catalyzer 16 is preferably arranged as a SCR catalyzer, which requires a reagent, for example ammoniac, for the conversion.

The reagent or a prestage of the reagent, for example a urea-water-solution, is preferably inserted directly in the exhaust gas area 12 upstream before the catalyzer 16. The dosage quantity is determined with the dosage signal s_D by the controller 20 depending on at least one dosage for the NOx emissions of the combustion engine 10 NOx_vK.

Such a dosage for the NOx emissions NOx_vK is calculated instead of a direct measurement preferably with the aid of e.g. at least one parameter of the combustion engine 10, for example the engine speed and/or a fuel signal.

In the shown embodiment it is assumed that the dosage signal s_D is determined within a pre-controlling, which is contained in a regulation 30. Furthermore it is presumed that the pre-controlling or rather the regulation of the dosage signal s_D takes place on grounds of the reagent filling-level in the catalyzer 16, which shall be defined to a reagent filling-level nominal value Fuel_Sol. Since the reagent filling-level actual value is metrologically not accessible without further ado, the actual value of the reagent filling-level shall be provided as a calculated reagent filling-level actual value Fuel_Sim.

The calculation takes place with the aid of a catalyzer model 32, which is provided with e.g. the temperature of the catalyzer, the NOx emissions NOx_vK as well as the dosage signal s_D. The catalyzer model 32 as well as the calculation of the reagent filling-level in the catalyzer 16 can be taken from the that have been described in detail in the beginning of the state of the art.

The pre-controlling in the regulation 30 determines a correcting variable s depending on the difference between the reagent filling-level nominal value Fuel_Sol and the calculated reagent filling-level actual value Fuel_Sim. The correcting variable s becomes the dosage signal s_D after a pass of the signal correction 34. Due to the not effectively present response of a measured actual value—the reagent filling-level actual value—it is here proceeded from a pre-controlling instead of a regulation onto the reagent filling-level nominal value Fuel_Sol.

The pre-controlling is superimposed by a regulation, which is able to compensate tolerances and drifts that are contingent upon component parts. In the shown embodiment it is assumed that the regulation is based on the NOx concentration NOx_nK that occurs downstream after the catalyzer 16, which is d by the NOx sensor 18 to the controller 20 as a NOx actual value NOx_Mes, whereby the NOx actual value NOx_Mes reflects at least a measure for the NOx concentration NOx_nK that occurs downstream after the catalyzer 16.

In the embodiment it is assumed that the regulation is based on a change of the reagent filling-level in the catalyzer 16. Furthermore it is assumed that the regulation considers the difference that occurs between the NOx actual value NOx_Mes and a NOx nominal value NOx_Sol.

One embodiment provides a short-term adaptation, which provides a short-term adaptation signal Adapt_K_ti depending for example on the difference d. The short-term adaptation signal Adapt_K_ti is determined in a short-term adaptation signal detection 38 depending on the difference d and provided for example for the catalyzer model 32 as short-term adaptation signal Adapt_K_ti, so that it can be intervened at short notice in the provision of the dosage signal s_D by a change of the calculated reagent filling-level actual value Fuel_Sim. Thereby it can be reacted at short notice to the underdosing as well as an overdosing.

A further embodiment, which can be provided alternatively or additionally, provides a long-term adaptation, which provides a long-term adaptation signal Adapt_L_ti that is also depending for example on the difference d. The long-term adaptation signal Adapt_L_ti is determined in a long-term adaptation signal detection 40 depending on the difference d and used for example in the signal correction 34 for correction the correction variable s as a long-term adaptation signal Adapt_L_ti. The signal correction 34 provides afterwards the dosage signal s_D.

It is assumed that the NOx sensor 18 shows a cross sensitivity towards the reagent. This means that initially it can not be differentiated between a too low dosage of the reagent, which causes that the undesired NOx concentration NOx_nK increases, and a too high reagent dosage, which causes that a reagent slip NH3 occurs.

In FIG. 2 the coherence between the dosage signal s_D and the NOx concentration NOx_nK on the one hand and between the dosage signal s_D and the reagent slip NH3 on the other hand is qualitatively shown. The NOx actual value NOx_Mes passes a minimum while crossing from a too low to a too high dosage.

The dosage of the reagent is preferably undertaken with the dosage signal s_D in a way that a NOx concentration NOx_nK as minimal as possible occurs simultaneously with a reagent slip NH3 that is as minimal as possible. In FIG. 2 a dosage signal starting value s_D_St is registered, which shall emerge from the starting-up of the NOx sensor 18, when the reagent filling-level shows the reagent filling-level nominal value Fuel_Sol and simultaneously the NOx actual value NOx_Mes and the NOx nominal value NOx_Sol correspond.

During the operation of the combustion engine 10 or rather the exhaust gas treatment device 14, 16, 18 it can not be excluded that the NOx sensor 18 is subject to a signal drift, which causes that the measured NOx actual value NOx_Mes does not correspond anymore with the actually present NOx concentration NOx_nK. Furthermore it has to be figured on a drift of the other components 14, 16 of the exhaust gas treatment device 14, 16, 18. The reagent insertion device 14, which is composed of several mechanic components, can be subject to a drift, which causes that the dosed reagent amount deviates from amount that has been predetermined by the dosage signal s_D. Furthermore the catalyzer 16 is subject to an ageing, which causes that for example more reagent is required with an advancing ageing. Furthermore it has to be figured on the NOx emissions of the combustion engine 10 to be subject to a long-term drift.

In order to ensure the compliance with a NOx concentration NOx_nK that is as low as possible during the entire operating time of the exhaust gas treatment device 14, 16, 18, it is provided to increase the dosage of the reagent with an advancing operating time of the exhaust gas treatment device 14, 16, 18. The operating time of the exhaust gas treatment device 14, 16, 18 corresponds generally with the operating time of the entire system, including the operating time of the combustion engine 10. In the following it is only referred to the operating time of the exhaust gas treatment device 14, 16, 18. The dosage signal s_D is influenced by a correcting signal k_Sol depending on a dosage for the operating time of the exhaust gas treatment device 14, 16, 18 in the sense of an increasing of the dosage of the reagent.

The correcting signal k_Sol provides a correcting signal detection 42 depending on the operating time of the exhaust gas treatment device 14, 16, 18. At the start-up of the exhaust gas treatment device 14, 16, 18 the correcting signal k_Sol is preferably set to a correcting signal starting value k_St 1. At this the dosage signal starting value s_D_St will adjust. The change of the correcting signal k_Sol takes place for example depending on the operating hours h of the exhaust gas treatment device 14, 16, 18. As long as the combustion engine 10 is provided for the power train of a motor vehicle, the driving distance km that has been covered by the motor vehicle can be used as the dosage for the operating time of the exhaust gas treatment device 14, 16, 18 alongside the operating hours of the combustion engine 10.

The consideration of the correcting signal k_Sol takes place in a nominal value correction 44, which connects the NOx nominal value NOx_Sol with the correcting signal k_Sol and provides a corrected nominal value NOx_k_Sol. The connection preferably happens multiplicatively, so that at the beginning of the operating time of the exhaust gas treatment device 14, 16, 18 no correction takes place and with an advancing operating time of the exhaust gas treatment device 14, 16, 18 a advancing correction takes place, which tendentially causes an increase of the dosage of the reagent.

The corrected NOx nominal value NOx_k_Sol is provided for a summarizer 46, which determines the difference between the corrected NOx nominal value NOx_k_Sol and the NOx actual value NOx_Mes and provides the difference d. The difference d intervenes the regulation 30 or rather the pre-controlling by e.g. an increase of the reagent filling-level nominal value Fuel_Sol and influences the correcting variable s. An increase of the corrected NOx nominal value NOx_k_Sol causes an increase of the correcting variable s and thereby an increase of the dosage signal s_D. The increase of the dosage of the reagent is figured in FIG. 2 with an arrow 50.

The influencing of the dosage signal s_D in the sense of an increase of the dosage with an advancing operating time of the exhaust gas treatment device 14, 16, 18 initially ensures that during a drift of the NOx sensor, at which the measured NOx actual value NOx_Mes is lower than the actual NOx concentration NOx_nK, a sufficient dosage of the reagent still takes place in order to comply with an preset minimum NOx conversion rate. If a drift of the NOx sensor 18, at which the measured NOx actual value NOx_Mes is higher than the actual NOx concentration NOx_nK, has occurred, still no increased reagent slip NH3 has to be accepted with an advancing operating time of the exhaust gas treatment device 14, 16, 18, because an overdosing due to the cross sensitivity of the NOx sensor 18 towards the reagent can be regulated.

The measure that is provided according to the invention still allows the compliance of a preset minimum NOx conversion rate, if admittedly the NOx sensor 18 works within the allowed tolerance area, however a drift within the remaining components 14, 16 of the exhaust gas treatment device 14, 16, 18 and/or a change of the NOx emissions that have been emitted by the combustion engine 10 occur. Even in this case, without the measure that is provided according to the invention, even with a properly working NOx sensor 18, it would not be excluded that the preset minimum NOx conversion rate is not complied with.

Altogether a weakness of the entire system regarding an underdosing of the reagent is compensated with the measure that is provided according to the invention—an overdosing of the reagent that advances tendentially with the operating time of the exhaust gas treatment device 14, 16, 18—without the need for accepting an unnecessary overdosing due to the robustness of the entire system regarding an overdosing of the reagent, since even a tolerance afflicted NOx sensor 18 registers short-term reagent breakthrough peaks due to its cross sensitivity towards the reagent.

The values range, in which the correcting signal k_Sol shall lie, can be determined with the aid of an assessment of the anticipated drifts. The values range lies for example between 1 and 1.2. The value 1 corresponds with the value during the start-up of the exhaust gas treatment device 14, 16, 18 and the value 1.2 with the value of the maximally expected operating time of the exhaust gas treatment device 14, 16, 18. Thereby it is assumed that the value 1 does not influence the NOx nominal value NOx_Sol and that the value 1.2 increases the NOx nominal value NOx_Sol up to the corrected NOx nominal value NOx_k_Sol, whereby the dosage of the reagent increases with an advancing operating time h, km of the exhaust gas treatment device 14, 16, 18 or the operating time of the entire system including the combustion engine 10. 

1. Procedure for operating an exhaust gas treatment device (14, 16, 18) arranged in the exhaust gas area (12) of a combustion engine (10), which requires for the catalytically supported conversion of the NOx emissions (NOx_vK) of the combustion engine (10) a reagent, whose dosage is determined by a dosage signal (s_D) depending on a NOx actual value (NOx_Mes) that is contained in the exhaust gas treatment device (14, 16, 18) and that is measured by a NOx sensor (18), which is contained in the exhaust gas treatment device (14, 16, 18) downstream after a catalyzer (16), is thereby characterized, in that the dosage signal (s_D) is influenced by a correcting signal (k_Sol) depending on a measure (h, km) for the operating time of the exhaust gas treatment device (14, 16, 18) in the sense of an increase of the dosage of the reagent.
 2. Procedure according to claim 1 is thereby characterized, in that the dosage signal (s_D) is pre-controlled and regulated.
 3. Procedure according to claim 2 is thereby characterized, in that the dosage signal (s_D) is pre-controlled with the aid of a calculated reagent filling-level actual level (Fuel_Sim) in the catalyzer (16).
 4. Procedure according to claim 3 is thereby characterized, in that the calculated reagent filling-level actual value (Fuel_Sim) is calculated with the aid of a catalyzer model (32), which considers at least the catalyzer temperature (te_Kat) as well as a measure for the NOx emissions (NOx_vK) of the combustion engine (10).
 5. Procedure according to claim 3 is thereby characterized, in that the difference (d) between the NOx actual value (NOx_Mes) and a NOx nominal value (NOx_Sol) is regulated.
 6. Procedure according to claim 5 is thereby characterized, in that the difference (d) influences the calculated reagent filling-level actual value (Fuel_Sim).
 7. Procedure according to claim 2 or 5 is thereby characterized, in that a short-term adaptation is provided, which intervenes the catalyzer model (32) at the calculation of the reagent filling-level actual value (Fuel_Sim) in the catalyzer (16) with a short-term adaptation signal (Adapt_K_ti).
 8. Procedure according to claim 2 or 5 is thereby characterized, in that a long-term adaptation is provided, which corrects a correcting variable (s) to a dosage signal (s_D) with a long-term adaptation signal (Adapt_L_ti).
 9. Procedure according to claim 5 is thereby characterized, in that the correcting signal (k_Sol) corrects the NOx nominal value (NOx_Sol).
 10. Procedure according to claim 3 is thereby characterized, in that the correcting signal (k_Sol) corrects a reagent filling-level nominal value (Fuel_Sol).
 11. Procedure according to claim 1 is thereby characterized, in that the covered distance (km) of a motor vehicle is used as a measure (h, km) for the operating time of the exhaust gas treatment device (14, 16, 18), in which the combustion engine (10) is used as power train.
 12. Procedure according to claim 1 is thereby characterized, in that the correcting signal (k_Sol) starts with the value 1 and increases up to the value 1.2.
 13. Device for operating an exhaust gas treatment device (14, 16, 18) arranged in the exhaust gas area (12) of a combustion engine (10), which requires for the catalytically supported conversion of the NOx emissions (NOx_vK) of the combustion engine (10) a reagent, whose dosage is determined by a dosage signal (s_D) depending on a NOx actual value (NOx_Mes) that is contained in the exhaust gas treatment device (14, 16, 18) and that is measured by a NOx sensor (18), which is contained in the exhaust gas treatment device (14, 16, 18) downstream after a catalyzer (16), is thereby characterized, in that at least one customized controller (20) for the implementation of the procedure according to the claims in 1 to 12 is provided.
 14. Control unit program, which implements all steps of a procedure according to one of the claims in 1 to 12, if the program runs in a controller (20).
 15. Control unit program with a program code, which is saved on a machine readable medium, for the implementation of the procedure according to one of the claims in 1 to 12, if the program runs in a controller (20). 